The invention relates generally to electronic assembly technology and more specifically to forming a refractory hydride films or layers under bump metallization structures.
One method of coupling bonding-pads of an integrated circuit chip to a package is by forming a metal bump (e.g., tin-lead (Snxe2x80x94Pb) solder bump) on each pad and soldering the substrate to a package. IBM calls its version of this technology controlled collapse chip connection (C4).
Improvements in the area of bump metallization include incorporating an under bump metallization (UBM) layer onto a chip. An UBM layer acts as a barrier preventing elements from diffusing between pad on a substrate and the bump that connects a bump chip and its packaging substrate. Additionally, an UBM layer improves adhesion between the bump and the pad on a substrate. Moreover, an UBM layer may act as a wetting layer that ensures improved chip joint properties between a solder-based bump and the pad on the substrate. These advantages apply to an UBM layer comprising a two layer structure A/Bxe2x80x94C, wherein A is, for example, a non-refractory metal such as gold or nickel and Bxe2x80x94C is a binary metal alloy such as titanium/tungsten (Ti/W), or a three layer structure A/B/C wherein A is a nonrefractory metal and B and C are refractory metals.
Refractory metals and their nitrides, such as titanium (Ti) and titanium nitride (TiN) are widely used as adhesion promoter and diffusion barrier layers in UBM. A refractory metal nitride layer such as TiN can be formed by depositing TiN via physical sputtering or chemical vapor deposition or annealing refractory metal in an N2 or NH3 ambient at temperatures up to 700xc2x0 C. However, high temperature back-end processing can lead to serious reliability related failure, especially in a chip using copper-based interconnects.
Several other disadvantages exist with processes known in the art. One problem is that interdiffusion of elements occurs between a bump and a pad when a packaged chip operates at a higher temperature. This causes the UBM layer to react with tin (Sn) contained in solder to form intermetallic compounds that are mechanically and electrically harmful to chip joints. The interfacial reaction at the bump/UBM interface can lead to delamination of the UBM layer on a pad, inducing chip malfunction. Moreover, electromigration (EM) induced failure may result at the bump/UBM interface from using known methods due to xe2x80x9cvoidsxe2x80x9d forming near the interface of the solder bump materials such as tin-lead (Snxe2x80x94Pb) and UBM materials when a high current is imposed on a bump at 100xc2x0 C. It is therefore desirable to simplify the process of forming UBM layers and generally improve the effectiveness of the UBM layer.
In one embodiment, a method is disclosed including forming a refractory layer over a pad coupled to a substrate and annealing the refractory layer in ambient hydrogen.